Surface preparation is a key factor in the bonding of two or more materials. Since bonding occurs at the surface of the two materials to be bonded, the condition of those surfaces are of critical importance. The foregoing is particularly true for the cases involving the bonding of at least one metallic surface (e.g., composites-to-metal, glass-to-metal, etc.) with an adhesive. The quality, and hence reliability, of boding of the materials achieved will be directly related to the surface roughness and cleanliness of the surfaces to be bonded.
The preparation of metallic surfaces for adhesive bonding is typically accomplished by one of two methods well known in the industry: phosphoric acid etching or sulfuric acid etching. For example, as the names suggest, Phosphoric Acid Anodizing (PAA), Phosphoric Acid Non-Tank Anodizing (PANTA) and Phos-Anodizing Containment System (PACS) methods of surface preparation all employ phosphoric acid etching. On the other hand, the Forest Product Laboratory (FPL) method of metallic surface preparation utilizes sulfuric acid etching.
Use of these existing techniques pose serious health and environmental problems. The threat presented by the use of toxic substances in these prior art techniques has resulted in current Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) policies to reduce, and eventually eliminate, the use of phosphoric and sulfuric acids for adhesive bonding purposes. Additionally, the existing methods often preclude simple and inexpensive preparation of the surface due to the complex procedures and equipment involved with the use of toxic substances. Finally, the exacting procedures and complicated equipment necessitated by use of toxic substances allows very little tolerance for error.
Thus a need has arisen for a safe, simple and inexpensive method of metallic surface preparation for adhesive bonding, whereby the use of complicated procedures and potentially dangerous toxic substances is significantly reduced or eliminated.